Tree Breeding

Tree Breeding

Seeks to improve the yield and quality through:-

  • Controlled pollination.
  • Breeding.
  • Extensive provenance and progeny testing and selections.
  • Reduction in rotation period.
  • Improvement in stem form.
  • Increase profitability for the forest industries.
  • Introduce new species for both commercial and social forestry.
  • Introduce latest propagation technologies.

Contribution of Tree Breeding Research to Climate Change Mitigation

The advent  of climate change has brought with it new challenges in tree improvement programs and as such Tree Breeders have been forced to shift their attention to tree species that are fast growing and can easily adapt to the changing environment. The major focus on tree improvement in Zimbabwe is mainly centered on exotic soft and hard woods namely the Pines and Eucalyptus species respectively. In response to this wake up call, the Tree Breeding Unit has embarked on a Breeding Programme to capacitate the forestry sector in light of climate change. In soft woods, the promising species are (P standing for pinus) – P maximinoii and P tecunumanii. These two species have shown great potential especially on growth rate and preliminary indications have shown that the two are outperforming P taeda, P elliottii and P oocarpa in their previously presumed niche areas. Research have shown that P tecunumanii, which is divided into two populations: high elevation population (>1500m.a.s.l) and low elevation population (<1500m.a.s.l), will soon prevent the monoculture of P patula in high altitude areas for the high elevation population and P elliottii and P oocarpa for the low elevation population. With climate change there is emergence of new pests and diseases as well as increased natural disturbances from native pests. To avoid catastrophic events on P patula which is the dominant species in the high altitude areas, P greggii, and P maximinoii were also introduced to reduce monoculture of P patula.
In addition to these fast-growing species, the unit is also working on P roxburghii for adaptability in low rainfall areas. Currently material for this species is coming from three provenances of the country with varying degree of aridness from where the species is showing average performance.
To augment these efforts, the unit is also working on Eucalyptus hybrids targeted mainly for the tobacco growing areas of the country. These have shown great potential in growth rate as well as adaptability. It is envisaged that this initiative will go a long way in providing fuel wood for curing tobacco without impacting negatively on the environment since they have a shorter growing period averaging five years from planting to harvesting. The hybrids are also suitable for plantation forestry and have an added advantage of reducing the rotation cycle due to their rapid growth rate.
Climate change has resulted in the large-scale movement of species and populations within species into climatic zones where they currently do not exist. The aim in tree improvement is to consider physiological adaptations of forest trees under various climate change scenarios. In this regard the Tree Breeding is emphasizing on breeding objectives of drought, disease and frost resistance in tree species. Breeding Eucalyptus hybrids is being conducted with the aim of providing suitable genotypes for planting in areas which are marginal for the parental species in terms of drought, frost and disease resistance.

Table1: Hybrids developed

Hybrid Cross (E- Eucalyptus) Breeding Objective
E grandis x E camaldulensis Drought, frost
E grandis x E tereticornis Drought, disease resistance
E grandis x  E saligna Fast growth
E grandis x E europhylla Disease resistance
E grandis x E pellita Fast growth, Disease resistance

 

Climate change brings a change in temperatures and this affects flowering phenology and abundance and hence seed production. Flowering studies are being conducted in P maximinoii and will be conducted in all new trials of P roxburghii.   Modern technologies such as vegetative propagation have been adopted to curb the issue of seeding shyness in certain species such as P maximinoii and P tecunumanii. The Forest Research Centre (FRC) has established a clonal hedge where superior genotypes are mass produced. To date there are 21 individuals for the E grandis x E tereticornis and 24 individuals for the E grandis x E camaldulensis hybrid represented in the clonal hedge at FRC.John Meikle Forest Research Station (JMFRS) is concentrating on vegetative propagation of Pinus species.

Table 2: Number of cuttings propagated at JMFRS

SPECIES GROWTH MEDIUM CUTTINGS WITH SERADIX CUTTINGS WITHOUT SERADIX
P caribaea x P tecunumanii Pine bark/Sand 220 348
P caribaea x P tecunumanii Pine bark/Sand 52 96
P tecunumanii Pine bark/Sand 59 96
P patula Pine bark/Sand 711 7519
P taeda Pine bark/Sand 48 35
P elliottii Pine bark/Sand 16 303
P maximinoii Pine bark/Sand 1211
Totals 1106 13184
Grand Total                14 290

Research into forestry species for the dry zones focuses on the objectives of fuelwood and building wood requirements by establishing tree plantations in the semi-arid regions of the country. The aim is to introduce tree species suitable for introduction into tree, pasture, food crop systems with special emphasis on nitrogen fixing species for the production of forage, fuelwood and shade and with soil protection and improvement properties.

Table below summaries the trials established.

Table 3: Trials established under the dry zone research

Trial No Type Species Location
EV133A Provenance Azadirachata indica Matopos
EV133B Provenance Azadirachata indica Ntabazinduna
EV133C Provenance Azadirachata indica Gwanda
EV133D Provenance Azadirachata indica Forest Hill
EX132 Progeny/
Provenance
F.albida Matopos
EV128C Provenance Acacia aneura Ntabazinduna
EV131 Provenance Acacia erioloba Matopos
EV136B Provenance Acacia auriculiformis Kosi
EV138 Provenance Sesbania sesban Matopos
EV139 Provenance Sesbania goetzii Matopos
EB45 Breeding Seedling Orchard E tereticornis Forest Hill
EB46 Breeding Seedling Orchard E tereticornis Forest Hill

Seven (7) F.albida progeny/provenance trials were established at Matopos, Chesa, Chibhero, Makaholi, Middle Sabi, Kadoma and Chesa. Current work is focused on eucalypts with the dominant species being Eucalyptus camaldulensis and Eucalyptus tereticornis.  The bulk of the work is done at Chesa Forest Station in Bulawayo (alt 1460m.asl, natural Region V (mean annual rainfall of 546mm).

The Breeding strategies being used combine genetic improvement of desired attributes and gene conservation. The tree improvement programme has 13 different pine species and 10 eucalyptus species undergoing improvement. The table below shows the number of seed orchards and the level of improvement of seed available in Zimbabwe for plantation and reforestation programmes.

Table 4: Number of seed orchards, area and level of improvement of seed germplasm available in Zimbabwe

Species Seed orchards
Number Generation Area (ha)
E grandis 6 2nd  and 4th 15
E camaldulensis 17 1st ,2nd,3rd and 4th 33
E tereticornis 9 2nd and 3rd 10
E citriodora 1 1st 0.6
P patula 26 1st and 2nd 46
P taeda 24 1st and 2nd 33
P elliottii 28 1st and 2nd 61
P kesiya 17 1st and 2nd 53
P oocarpa 7 1st 22
P pseudostrobus 1 1st 0.7
P maximinoii 4 1st 19
P tecunumanii 14 1st 18
P caribaea var hondurensis 1 1st 0.6
P caribaea var bahamensis 1 1st 0.6
P caribaea var
caribaea
1 1st 0.6
P palustris 1 1st 0.5
P chiapensis 4 1st 6
Pinus spp hybrids 2 1.4
Cupressus lusitanica 1 0.6
Total 165   321.6